Mucopolysaccharidosis IVA (Morquio A disease, MPS IVA) is a lysosomal storage disease in which there is a deficiency of the protein N-acetylgalactosamine-6-sulfate sulfatase (GALNS).1 It is a rare autosomal recessive disorder that affects about 1 in 250,000 live births.2 The accumulation of chondroitin-6-sulfate (C6S) and keratan sulfate (KS) results in systemic skeletal chondrodysplasia.1,3 ′Additional clinical manifestations of Morquio A disease include elevated blood and urine C6S and KS levels, hypoplasia of the odontoid process, pectus carinatum, marked short stature, knock knees, kyphoscoliosis, and corneal clouding.1 
In 2014, the FDA approved enzyme replacement therapy (ERT) for Morquio A disease based on limited improvement in the 6 minute walk test (Hendriksz, C. J., (2014) J Inherit Metab Dis 37(6):979-90). Enzyme replacement therapy replaces the deficient enzyme in an affected patient through intravenous infusion.4 This prevents the progression of MPS IVA; by increasing the concentration of GALNS in cells,4 however, it does not affect the causal mechanism of the defect. One challenge that is encountered is that the replaced enzyme is seen as foreign to the body and provokes an immune response. The immunogenic response develops in the patient against the replacement enzyme including hypersensitivity reactions, neutralizing antibodies, and modified enzyme targeting or turnover,6 all of which significantly decreases the efficacy of treatment. An immune response in human and animal models is developed in all available enzyme replacement therapies for lysosomal storage diseases, including the FDA approved ERTs. Preclinical trials of enzyme replacement therapy (ERT) in Mucopolysaccharidosis IVA (Morquio A disease, MPS IVA) has been shown to successfully treat the disease, but the immune response that accompanies this treatment significantly decreases efficacy. The patient may not develop tolerance until 2 to 3 years after their initial dose of ERT which results in 2 to 3 years of substandard therapy at an annual cost of ERT ranges from $200,000 to $500,000 per patient. The current approach to counteract the immune response with immunosuppressive protocols.6 However, this leaves the patient susceptible to infection, may result in drug-drug interactions, increases cost of therapy, in addition to other side effects. A number of factors including the nature of the infused protein, genetic background of the patient, route of enzyme administration, frequency and dose of treatment, as well as structural differences between the infused and the defective protein and environmental factors, may all contribute to this immune response which occurs during ERT in LSDs, and presents one of the major complications of this treatment.
Morquio A disease (MPS IVA), which involves a deficiency of the N-acetylgalactosamine-6-sulfate sulfatase (GALNS), is particularly affected. To alleviate immunoreactions associated with ERT for Morquio, the Inventors have bioengineered variants of the GALNS protein with reduced immunogenicity and without a significant loss of biological activity. Using the FASTA format of the GALNS sequences and computational programs, the Inventors have evaluated predictions of the immunogenicity, post-translational modifications, physic chemical properties, and molecular docking, thus allowing them to rapidly narrow 324 potential modified GALNS sequences to 7 modified GALNS sequences predicted to contain properties most similar to the original GALNS protein. In vitro studies were performed by transfection of HEK293 cells with cDNA of the seven sequences. Results indicate that three out of seven mutated GALNS sequences retained 80% or more enzyme activity relative to the wild type GALNS in vitro. Production of the modified GALNS sequences in COS-7 cells co-transfected with SUMF1 resulted in an additional increase in activity.
The development of a less immunogenic GALNS protein provides improved efficacy of ERT for treatment for MPS IV, and will alleviate the need for immunosuppressive protocols of ERT.